Freeform Varifocal Optical Assembly for HMD Aberration Correction
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Solution Overview
Problem
Head-mounted display devices for virtual and augmented reality often cause eye fatigue and discomfort due to imperfect accommodation and higher order aberrations, which lead to blurry vision and headaches, as they fail to provide adequate focus and aberration correction for individual users.
Innovation Solution
A freeform varifocal optical assembly with adjustable optical stages that can change focal lengths and optical powers for different polarizations, incorporating polarization-sensitive optical elements associated with Zernike polynomials to correct lower and higher order aberrations, allowing for customizable wavefront correction and accommodation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional fixed-focus optical systems are used in head-mounted displays, then the device structure is simple, but the user experiences eye fatigue and discomfort due to imperfect accommodation and higher order aberrations
Solution Approach 1:
The patent implements a varifocal optical system where the optical power can be dynamically adjusted between multiple focal points (e.g., infinity focus and near focus). This allows the system to adapt to different viewing distances and accommodation states, resolving the contradiction by making the optical system dynamic rather than fixed, thereby improving visual comfort without requiring overly complex adaptive mechanisms for every possible focal distance
Solution Approach 2:
The optical system is divided into multiple discrete optical stages, each capable of providing specific wavefront corrections for different Zernike polynomial terms (e.g., defocus, astigmatism, coma). By segmenting the aberration correction into separate adjustable stages, the system can address multiple visual defects independently, improving overall visual comfort while maintaining manageable system complexity through modular design
2Reliability
If multiple adjustable optical stages are implemented to correct aberrations, then visual comfort and accommodation are improved, but the device weight and size increase
Solution Approach 1:
The patent employs thin-film optical elements and compact optical designs that provide multiple aberration correction functions within minimal thickness and weight. The varifocal mechanism uses compact moving components or tunable optical elements that achieve focal adjustment without requiring large, heavy mechanical structures, thereby improving accommodation correction while minimizing added weight in the head-mounted display
Solution Approach 2:
Multiple optical stages that correct different types of aberrations (defocus, astigmatism, coma, spherical aberration) are merged into a single integrated optical assembly. This consolidation allows the system to provide comprehensive aberration correction and varifocal capability within one compact unit rather than requiring separate corrective elements, thereby improving accommodation correction while reducing overall device weight and size
3Reliability
If polarization-sensitive optical elements are used for wavefront correction, then higher order aberrations are corrected, but the manufacturing precision requirements increase
Solution Approach 1:
The patent uses optical elements whose properties can be tuned or adjusted after manufacturing (e.g., liquid crystal elements, deformable mirrors, or tunable lenses). This allows the system to achieve precise wavefront correction by adjusting optical parameters (focal length, aberration coefficients) rather than requiring extremely tight manufacturing tolerances, thereby improving aberration correction accuracy while reducing manufacturing precision requirements
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances user comfort and enjoyment by providing precise focus and aberration correction, reducing eye fatigue and the need for prescription optics, while allowing for adjustable optical power to suit individual eye conditions.
Implementation Method 1
Each optical module includes at least one polarization sensitive lensing element and may include a selected type of lensing (e.g., a selected type of optical aberration). By including a plurality of optical modules, each optical module including at least one polarization sensitive lensing element and controlling polarization of light incident to the polarization sensitive lensing elements
Implementation Method 2
The varifocal optical assembly includes an optical stack that can be configured to enhance the accommodation of one or both eyes of a display observer by providing focus and higher order aberration correction
Data Source
AI summary
A freeform varifocal optical assembly includes at least three optical modules including a first plurality of optical elements including Pancharatnam-Berry phase (PBP) lenses, polarization sensitive hologram (PSH) lenses, metamaterials, or combinations thereof. The plurality of optical elements of each optical module include a property associated with a Zernike polynomial. Each of the first and the three optical modules are configurable between a plurality of optical powers. The freeform varifocal optical assembly is configurable to output a predetermined wavefront in response to an input wavefront.